This invention relates to a hollow fan blade for the fan of an aircraft engine with cavities provided in the blade for weight reduction and, further, to a method for the manufacture of such a blade.
The fan blades are the foremost rotating components of an aircraft engine and are, therefore, subject to considerable loads by ingested foreign bodies, such as birds, primarily in the take-off phase. In order to withstand the extremely high loads, the fan blades are made of a high-strength metal, metal alloy or fiber-reinforced polymer with metallic leading edge protection and dimensioned adequately. Such solid blades are, on the one hand, very costly due to the high amount of expensive material invested and, on the other hand, the mechanical loads arising from natural vibrations, vibration amplitude and centrifugal forces are high. Furthermore, the fan containments must be dimensioned commensurate with the high weight of solid blades, this entailing a further increase in weight of the aircraft engine and additional costs.
For high-power aircraft engines, hollow fan blades, i.e. fan blades with inner cavities, have already been developed to save weight and to avoid the disadvantages resulting from a high weight. The known hollow blades according to Patents U.S. Pat. No. 5,692,881 and U.S. Pat. No. 6,033,186, for example, which are known as fabricated structures, require, however, complicated and accordingly costly forming and joining techniques for their production.
It has also been proposed to provide the blade with long cavities originating at the blade tip and extending towards the blade root and to produce these cavities by means of known material removal processes, such as ECM (electro-chemical machining) or EDM (electro-discharge machining). This method, or the blades produced by this method, is/are, however, disadvantageous in that the cavities, due to the curvature of the blades, can only be produced in a limited tip area, as a result of which the weight saving and cost reduction effect is minimal.